Mitochondrial complex I derived ROS regulate stress adaptation in Drosophila melanogaster

Alleviating effect of methionine on intestinal mucosal injury induced by heat stress

Climate change is an increasing concern of stakeholders worldwide. The intestine is severely impacted by the heat stress. This study aimed to investigate the alleviating effects of methionine on the intestinal damage induced by heat stress in mice. The mice were divided into four groups: control group (C), methionine deficiency group (MD), methionine + heat stress group (MH), and methionine deficiency + heat stress group (MDH). Histopathological techniques, PAS-Alcian blue staining, immunohistochemistry method, biochemical quantification method, ELISA, and micro method were used to study the changes in the intestinal mucosal morphology, the number of goblet cells, the expression of tight junction proteins, the peroxide product contents and antioxidant enzyme activities, the intestinal mucosal damage, the content of immunoglobulins and HSP70, the activity of Na+/K+-ATPase. The results showed that methionine can improve intestinal mucosal morphology (increase the villi height, V/C value, and muscle layer thickness, decrease crypt depth), increase the expression of tight junction proteins (Claudin-1, Occludin, ZO-1) and the content of DAO, decrease the content of intestinal mucosa damage markers (ET, FABP2) and peroxidation products (MDA), increase the activity of antioxidant enzymes (GR, GSH-Px, SOD), the number of goblet cells, the contents of immunoglobulins (sIgA, IgA, IgG, IgM) and stress protein (HSP70), and the activity of Na+/K+-ATPase. It is suggested that methionine can alleviate intestinal damage in heat-stressed mice.

Mitochondrial redox state, bioenergetics, and calcium transport in caloric restriction: A metabolic nexus

Mitochondria congregate central reactions in energy metabolism, many of which involve electron transfer. As such, they are expected to both respond to changes in nutrient supply and demand and also provide signals that integrate energy metabolism intracellularly. In this review, we discuss how mitochondrial bioenergetics and reactive oxygen species production is impacted by dietary interventions that change nutrient availability and impact on aging, such as calorie restriction. We also discuss how dietary interventions alter mitochondrial Ca2+ transport, regulating both mitochondrial and cytosolic processes modulated by this ion. Overall, a plethora of literature data support the idea that mitochondrial oxidants and calcium transport act as integrating signals coordinating the response to changes in nutritional supply and demand in cells, tissues, and animals.

Impact of Mitochondrial Architecture, Function, Redox Homeostasis, and Quality Control on Organismic Aging: Lessons from a Fungal Model System

Significance: Mitochondria are eukaryotic organelles with various essential functions. They are both the source and the targets of reactive oxygen species (ROS). Different branches of a mitochondrial quality control system (mQCS), such as ROS balancing, degradation of damaged proteins, or whole mitochondria, can mitigate the adverse effects of ROS stress. However, the capacity of mQCS is limited. Overwhelming this capacity leads to dysfunctions and aging. Strategies to interfere into mitochondria-dependent human aging with the aim to increase the healthy period of life, the health span, rely on the precise knowledge of mitochondrial functions. Experimental models such as Podospora anserina, a filamentous fungus with a clear mitochondrial aging etiology, proved to be instrumental to reach this goal. Recent Advances: Investigations of the P. anserina mQCS revealed that it is constituted by a complex network of different branches. Moreover, mitochondrial architecture and lipid homeostasis emerged to affect aging. Critical Issues: The regulation of the mQCS is only incompletely understood. Details about the involved signaling molecules and interacting pathways remain to be elucidated. Moreover, most of the currently generated experimental data were generated in well-controlled experiments that do not reflect the constantly changing natural life conditions and bear the danger to miss relevant aspects leading to incorrect conclusions. Future Directions: In P. anserina, the precise impact of redox signaling as well as of molecular damaging for aging remains to be defined. Moreover, natural fluctuation of environmental conditions needs to be considered to generate a realistic picture of aging mechanisms as they developed during evolution.

Fatty acid oxidation drives mitochondrial hydrogen peroxide production by α-ketoglutarate dehydrogenase

In the present study, we examined the mitochondrial hydrogen peroxide (mH2O2) generating capacity of α-ketoglutarate dehydrogenase (KGDH) and compared it to components of the electron transport chain using liver mitochondria isolated from male and female C57BL6N mice. We show for the first time there are some sex dimorphisms in the production of mH2O2 by electron transport chain complexes I and III when mitochondria are fueled with different substrates. However, in our investigations into these sex effects, we made the unexpected and compelling discovery that 1) KGDH serves as a major mH2O2 supplier in male and female liver mitochondria and 2) KGDH can form mH2O2 when liver mitochondria are energized with fatty acids but only when malate is used to prime the Krebs cycle. Surprisingly, 2-keto-3-methylvaleric acid (KMV), a site-specific inhibitor for KGDH, nearly abolished mH2O2 generation in both male and female liver mitochondria oxidizing palmitoyl-carnitine. KMV inhibited mH2O2 production in liver mitochondria from male and female mice oxidizing myristoyl-, octanoyl-, or butyryl-carnitine as well. S1QEL 1.1 (S1) and S3QEL 2 (S3), compounds that inhibit reactive oxygen species generation by complexes I and III, respectively, without interfering with OxPhos and respiration, had a negligible effect on the rate of mH2O2 production when pyruvate or acyl-carnitines were used as fuels. However, inclusion of KMV in reaction mixtures containing S1 and/or S3 almost abolished mH2O2 generation. Together, our findings suggest KGDH is the main mH2O2 generator in liver mitochondria, even when fatty acids are used as fuel.

The endogenous antioxidant ability of royal jelly in Drosophila is independent of Keap1/Nrf2 by activating oxidoreductase activity

Royal jelly (RJ) is a biologically active substance secreted by the hypopharyngeal and mandibular glands of worker honeybees. It is widely claimed that RJ reduces oxidative stress. However, the antioxidant activity of RJ has mostly been determined by in vitro chemical detection methods or by external administration drugs that cause oxidative stress. Whether RJ can clear the endogenous production of reactive oxygen species (ROS) in cells remains largely unknown. Here, we systematically investigated the antioxidant properties of RJ using several endogenous oxidative stress models of Drosophila. We found that RJ enhanced sleep quality of aging Drosophila, which is decreased due to an increase of oxidative damage with age. RJ supplementation improved survival and suppressed ROS levels in gut cells of flies upon exposure to hydrogen peroxide or to the neurotoxic agent paraquat. Moreover, RJ supplementation moderated levels of ROS in endogenous gut cells and extended lifespan after exposure of flies to heat stress. Sleep deprivation leads to accumulation of ROS in the gut cells, and RJ attenuated the consequences of oxidative stress caused by sleep loss and prolonged lifespan. Mechanistically, RJ prevented cell oxidative damage caused by heat stress or sleep deprivation, with the antioxidant activity in vivo independent of Keap1/Nrf2 signaling. RJ supplementation activated oxidoreductase activity in the guts of flies, suggesting its ability to inhibit endogenous oxidative stress and maintain health, possibly in humans.

Effect of exercise on improving myocardial mitochondrial function in decreasing diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM) is a significant cause of heart failure in patients with diabetes, and its pathogenesis is closely related to myocardial mitochondrial injury and functional disability. Studies have shown that the development of diabetic cardiomyopathy is related to disorders in mitochondrial metabolic substrates, changes in mitochondrial dynamics, an imbalance in mitochondrial Ca2+ regulation, defects in the regulation of microRNAs, and mitochondrial oxidative stress. Physical activity may play a role in resistance to the development of diabetic cardiomyopathy by improving myocardial mitochondrial biogenesis, the level of autophagy and dynamic changes in fusion and division; enhancing the ability to cope with oxidative stress; and optimising the metabolic substrates of the myocardium. This paper puts forward a new idea for further understanding the specific mitochondrial mechanism of the occurrence and development of diabetic cardiomyopathy and clarifying the role of exercise-mediated myocardial mitochondrial changes in the prevention and treatment of diabetic cardiomyopathy. This is expected to provide a new theoretical basis for exercise to reduce diabetic cardiomyopathy symptoms.

Involvement of Sep38β in the Insecticidal Activity of Bacillus thuringiensis against Beet Armyworm, Spodoptera exigua (Lepidoptera)

The p38 mitogen-activated protein kinases (MAPKs) are associated with insect immunity, tissue repair, and the insecticidal activity of Bacillus thuringiensis (Bt). Here, a p38 MAPK family gene (Sep38β) was identified from Spodoptera exigua. Among the developmental stages, the transcription level of Sep38β was the highest in egg, followed by that in prepupa and pupa. Sep38β expression peaked in Malpighian tubules and the hemolymph of fifth instar larvae. Knockdown of Sep38β or injection of SB203580 (a p38 MAPK inhibitor) significantly downregulated the SeDUOX expression and reactive oxygen species (ROS) level in the midgut, accounting for deterioration of the midgut to scavenge pathogens and enhancement of Bt insecticidal activity. In conclusion, all the results demonstrate that Sep38β regulates the immune-related ROS level in the insect midgut, which suppresses the insecticidal activity of Bt against S. exigua by 17-22%. Our study highlights that Sep38β is essential for insect immunity and the insecticidal activity of Bt to S. exigua and is a potential target for pest control.

Mitochondrial complex I ROS production and redox signaling in hypoxia

Mitochondria are a main source of cellular energy. Oxidative phosphorylation (OXPHOS) is the major process of aerobic respiration. Enzyme complexes of the electron transport chain (ETC) pump protons to generate a protonmotive force (Δp) that drives OXPHOS. Complex I is an electron entry point into the ETC. Complex I oxidizes nicotinamide adenine dinucleotide (NADH) and transfers electrons to ubiquinone in a reaction coupled with proton pumping. Complex I also produces reactive oxygen species (ROS) under various conditions. The enzymatic activities of complex I can be regulated by metabolic conditions and serves as a regulatory node of the ETC. Complex I ROS plays diverse roles in cell metabolism ranging from physiologic to pathologic conditions. Progress in our understanding indicates that ROS release from complex I serves important signaling functions. Increasing evidence suggests that complex I ROS is important in signaling a mismatch in energy production and demand. In this article, we review the role of ROS from complex I in sensing acute hypoxia.

Clonal MDS/AML cells with enhanced TWIST1 expression reprogram the differentiation of bone marrow MSCs

Bone marrow-derived mesenchymal stem cells (BMMSCs) derived from myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) patients often show a shift in the balance between osteoblastogenesis and adipogenesis. It was suggested that BMMSCs can potentially undergo reprogramming or educational processes. However, the results of reprogrammed differentiation have been inconclusive. In this study, clinical samples, co-culture models and mouse models were employed to explore the association of MDS/AML clonal cells and BMMSCs differentiation. We found that clonal MDS/AML cells promoted adipogenic differentiation and inhibited osteogenic differentiation of BMMSCs, which in turn promoted MDS expansion. Mass spectrometry and cytokine array were used to identify the molecules to drive the BMMSCs differentiation in MDS/AML. Mechanistically, highly expressed transcription factor TWIST1 in clonal MDS/AML cells induces MDS/AML cells to secrete more IFN-γ, which can induce oxidative stress through STAT1-dependent manner, ultimately causing enhanced adipogenic differentiation and inhibited osteogenic differentiation in BMMSCs. Overall, our findings suggest that targeting the driving oncogenes in malignant clonal cells, such as TWIST1, may offer new therapeutic strategies by remodeling the surrounding bone marrow microenvironment in the treatment of MDS/AML and other hematopoietic malignancies.

Bypassing mitochondrial defects rescues Huntington's phenotypes in Drosophila

Huntington's disease (HD) is a fatal neurodegenerative disease with limited treatment options. Human and animal studies have suggested that metabolic and mitochondrial dysfunctions contribute to HD pathogenesis. Here, we use high-resolution respirometry to uncover defective mitochondrial oxidative phosphorylation and electron transfer capacity when a mutant huntingtin fragment is targeted to neurons or muscles in Drosophila and find that enhancing mitochondrial function can ameliorate these defects. In particular, we find that co-expression of parkin, an E3 ubiquitin ligase critical for mitochondrial dynamics and homeostasis, produces significant enhancement of mitochondrial respiration when expressed either in neurons or muscles, resulting in significant rescue of neurodegeneration, viability and longevity in HD model flies. Targeting mutant HTT to muscles results in larger mitochondria and higher mitochondrial mass, while co-expression of parkin increases mitochondrial fission and decreases mass. Furthermore, directly addressing HD-mediated defects in the fly's mitochondrial electron transport system, by rerouting electrons to either bypass mitochondrial complex I or complexes III-IV, significantly increases mitochondrial respiration and results in a striking rescue of all phenotypes arising from neuronal mutant huntingtin expression. These observations suggest that bypassing impaired mitochondrial respiratory complexes in HD may have therapeutic potential for the treatment of this devastating disorder.

Changes in the Mitochondria in the Aging Process-Can α-Tocopherol Affect Them?

Aerobic organisms use molecular oxygen in several reactions, including those in which the oxidation of substrate molecules is coupled to oxygen reduction to produce large amounts of metabolic energy. The utilization of oxygen is associated with the production of ROS, which can damage biological macromolecules but also act as signaling molecules, regulating numerous cellular processes. Mitochondria are the cellular sites where most of the metabolic energy is produced and perform numerous physiological functions by acting as regulatory hubs of cellular metabolism. They retain the remnants of their bacterial ancestors, including an independent genome that encodes part of their protein equipment; they have an accurate quality control system; and control of cellular functions also depends on communication with the nucleus. During aging, mitochondria can undergo dysfunctions, some of which are mediated by ROS. In this review, after a description of how aging affects the mitochondrial quality and quality control system and the involvement of mitochondria in inflammation, we report information on how vitamin E, the main fat-soluble antioxidant, can protect mitochondria from age-related changes. The information in this regard is scarce and limited to some tissues and some aspects of mitochondrial alterations in aging. Improving knowledge of the effects of vitamin E on aging is essential to defining an optimal strategy for healthy aging.

Piranhea trifoliata extracts ameliorate muscular decline in Drosophila melanogaster exposed to Paraquat

In this study, we have demonstrated, for the first time, the muscular protective effects of Piranhea trifoliata bark extract against Paraquat (PQ)-induced oxidative stress in Drosophila melanogaster. Exposure of D. melanogaster (Canton Special) to PQ caused oxidative stress, as evidenced by protein carbonyl and elevated acetylcholinesterase (AChE) activity levels. However, a diet supplemented with the P. trifoliata extracts (0.1 mg/ml) for 10 days ameliorates protein carbonyl levels and enzymatic activities of AChE and citrate synthase to prevent PQ damage. Also, P. trifoliata bark extracts showed in phytochemical assays the presence of phenols, at 46.06 mg EAG/g extract of total phenolic compounds, and a 40% 2,2-diphenyl-1-picryl-hydrazyl scavenging effect. The study showed the muscular protective function of the P. trifoliata extracts in D. melanogaster exposed to PQ. On the basis of the results, we contemplate that the bark of P. trifoliata might prevent and ameliorate human diseases caused by oxidative stress. The muscular action of the P. trifoliata extract can be attributed to the antioxidant constituents, while the precise mechanism of its action needs further investigation.

How the Disruption of Mitochondrial Redox Signalling Contributes to Ageing

In the past, mitochondrial reactive oxygen species (mtROS) were considered a byproduct of cellular metabolism. Due to the capacity of mtROS to cause oxidative damage, they were proposed as the main drivers of ageing and age-related diseases. Today, we know that mtROS are cellular messengers instrumental in maintaining cellular homeostasis. As cellular messengers, they are produced in specific places at specific times, and the intensity and duration of the ROS signal determine the downstream effects of mitochondrial redox signalling. We do not know yet all the processes for which mtROS are important, but we have learnt that they are essential in decisions that affect cellular differentiation, proliferation and survival. On top of causing damage due to their capacity to oxidize cellular components, mtROS contribute to the onset of degenerative diseases when redox signalling becomes dysregulated. Here, we review the best-characterized signalling pathways in which mtROS participate and those pathological processes in which they are involved. We focus on how mtROS signalling is altered during ageing and discuss whether the accumulation of damaged mitochondria without signalling capacity is a cause or a consequence of ageing.

Mitochondria Need Their Sleep: Redox, Bioenergetics, and Temperature Regulation of Circadian Rhythms and the Role of Cysteine-Mediated Redox Signaling, Uncoupling Proteins, and Substrate Cycles

Although circadian biorhythms of mitochondria and cells are highly conserved and crucial for the well-being of complex animals, there is a paucity of studies on the reciprocal interactions between oxidative stress, redox modifications, metabolism, thermoregulation, and other major oscillatory physiological processes. To address this limitation, we hypothesize that circadian/ultradian interaction of the redoxome, bioenergetics, and temperature signaling strongly determine the differential activities of the sleep–wake cycling of mammalians and birds. Posttranslational modifications of proteins by reversible cysteine oxoforms, S-glutathionylation and S-nitrosylation are shown to play a major role in regulating mitochondrial reactive oxygen species production, protein activity, respiration, and metabolomics. Nuclear DNA repair and cellular protein synthesis are maximized during the wake phase, whereas the redoxome is restored and mitochondrial remodeling is maximized during sleep. Hence, our analysis reveals that wakefulness is more protective and restorative to the nucleus (nucleorestorative), whereas sleep is more protective and restorative to mitochondria (mitorestorative). The “redox–bioenergetics–temperature and differential mitochondrial–nuclear regulatory hypothesis” adds to the understanding of mitochondrial respiratory uncoupling, substrate cycling control and hibernation. Similarly, this hypothesis explains how the oscillatory redox–bioenergetics–temperature–regulated sleep–wake states, when perturbed by mitochondrial interactome disturbances, influence the pathogenesis of aging, cancer, spaceflight health effects, sudden infant death syndrome, and diseases of the metabolism and nervous system.

Cryo-EM structures of mitochondrial respiratory complex I from Drosophila melanogaster

Respiratory complex I powers ATP synthesis by oxidative phosphorylation, exploiting the energy from NADH oxidation by ubiquinone to drive protons across an energy-transducing membrane. Drosophila melanogaster is a candidate model organism for complex I due to its high evolutionary conservation with the mammalian enzyme, well-developed genetic toolkit, and complex physiology for studies in specific cell types and tissues. Here, we isolate complex I from Drosophila and determine its structure, revealing a 43-subunit assembly with high structural homology to its 45-subunit mammalian counterpart, including a hitherto unknown homologue to subunit NDUFA3. The major conformational state of the Drosophila enzyme is the mammalian-type 'ready-to-go' active resting state, with a fully ordered and enclosed ubiquinone-binding site, but a subtly altered global conformation related to changes in subunit ND6. The mammalian-type 'deactive' pronounced resting state is not observed: in two minor states, the ubiquinone-binding site is unchanged, but a deactive-type π-bulge is present in ND6-TMH3. Our detailed structural knowledge of Drosophila complex I provides a foundation for new approaches to disentangle mechanisms of complex I catalysis and regulation in bioenergetics and physiology.

Protein S-glutathionylation and sex dimorphic effects on hydrogen peroxide production by dihydroorotate dehydrogenase in liver mitochondria

Dihydroorotate dehydrogenase (DHODH) oxidizes dihydroorotate to orotate for pyrimidine biosynthesis, donating electrons to the ubiquinone (UQ) pool of mitochondria. DHODH has a measurable rate for hydrogen peroxide (H₂O₂) production and thus contributes to cellular changes in redox tone. Protein S-glutathionylation serves as a negative feedback loop for the inhibition of H₂O₂ by several α-keto acid dehydrogenases and respiratory complexes in mitochondria, as well as ROS sources in liver cytoplasm. Here, we report this redox signaling mechanism also inhibits H₂O₂ production by DHODH in liver mitochondria isolated from male and female C57BL6N mice. We discovered that low amounts of the glutathionylation catalyst, disulfiram (50-500 nM), almost abolished H₂O₂ production by DHODH in mitochondria from male mice. Similar results were collected with diamide, however, higher doses (1000-5000 μM) were required to elicit this effect. Disulfiram and diamide also significantly suppressed H₂O₂ production by DHODH in female liver mitochondria. However, liver mitochondria from female mice were more resistant to disulfiram or diamide-mediated inhibition of H₂O₂ genesis when compared to samples from males. Analysis of the impact of disulfiram and diamide on DHODH activity revealed that both compounds inhibited the dehydrogenase directly, however the effect was less in female mice. Additionally, disulfiram and diamide impeded the use of dihydroorotate fueled oxidative phosphorylation in mitochondria from males and females, although samples collected from female rodents displayed more resistance to this inhibition. Taken together, our findings demonstrate H₂O₂ production by DHODH can be inhibited by glutathionylation and sex can impact this redox modification.

Regulation of Mitochondrial Hydrogen Peroxide Availability by Protein S-glutathionylation

BACKGROUND

It has been four decades since protein S-glutathionylation was proposed to serve as a regulator of cell metabolism. Since then, this redox-sensitive covalent modification has been identified as a cell-wide signaling platform required for embryonic development and regulation of many physiological functions.

SCOPE OF THE REVIEW

Mitochondria use hydrogen peroxide (H₂O₂) as a second messenger, but its availability must be controlled to prevent oxidative distress and promote changes in cell behavior in response to stimuli. Experimental data favor the function of protein S-glutathionylation as a feedback loop for the inhibition of mitochondrial H₂O₂ production.

MAJOR CONCLUSIONS

The glutathione pool redox state is linked to the availability of H₂O₂, making glutathionylation an ideal mechanism for preventing oxidative distress whilst playing a part in desensitizing mitochondrial redox signals.

GENERAL SIGNIFICANCE

The biological significance of glutathionylation is rooted in redox status communication. The present review critically evaluates the experimental evidence supporting its role in negating mitochondrial H₂O₂ production for cell signaling and prevention of electrophilic stress.

Luteolin alleviated damage caused by blue light to Drosophila

Short-wavelength blue light is commonly found in daily life and is harmful to health. In this experiment, we investigated the effect of luteolin on the survival time of Drosophila under the blue light condition of 3000 Lux using Drosophila as the model organism. The results showed that luteolin alleviated the damage suffered by Drosophila under blue light irradiation, significantly prolonged the survival time of Drosophila, prolonged the survival time of male Drosophila in the heat stress assay, increased the activity of female Drosophila in the spontaneous activity assay, and increased the egg production of female Drosophila at the highest concentration, and there was no significant difference in the food intake experiment. We suggest that the increase in survival time of Drosophila under blue light conditions is due to the function of luteolin in resisting oxidative stress.

WITHDRAWN: Mitochondria need their sleep: Sleep-wake cycling and the role of redox, bioenergetics, and temperature regulation, involving cysteine-mediated redox signaling, uncoupling proteins, and substrate cycles

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Rheumatoid arthritis and mitochondrial homeostasis: The crossroads of metabolism and immunity

Rheumatoid arthritis is an autoimmune disease characterized by chronic symmetric synovial inflammation and erosive bone destruction. Mitochondria are the main site of cellular energy supply and play a key role in the process of energy metabolism. They possess certain self-regulatory and repair capabilities. Mitochondria maintain relative stability in number, morphology, and spatial structure through biological processes, such as biogenesis, fission, fusion, and autophagy, which are collectively called mitochondrial homeostasis. An imbalance in the mitochondrial homeostatic environment will affect immune cell energy metabolism, synovial cell proliferation, apoptosis, and inflammatory signaling. These biological processes are involved in the onset and development of rheumatoid arthritis. In this review, we found that in rheumatoid arthritis, abnormal mitochondrial homeostasis can mediate various immune cell metabolic disorders, and the reprogramming of immune cell metabolism is closely related to their inflammatory activation. In turn, mitochondrial damage and homeostatic imbalance can lead to mtDNA leakage and increased mtROS production. mtDNA and mtROS are active substances mediating multiple inflammatory pathways. Several rheumatoid arthritis therapeutic agents regulate mitochondrial homeostasis and repair mitochondrial damage. Therefore, modulation of mitochondrial homeostasis would be one of the most attractive targets for the treatment of rheumatoid arthritis.

The effect of metformin on ameliorating neurological function deficits and tissue damage in rats following spinal cord injury: A systematic review and network meta-analysis

Spinal cord injury (SCI) is a devastating condition with few treatment options. Metformin, a classical antidiabetic and antioxidant, has extended its application to experimental SCI treatment. Here, we performed a systematic review to evaluate the neurobiological roles of metformin for treating SCI in rats, and to assess the potential for clinical translation. PubMed, Embase, China National Knowledge Infrastructure, WanFang data, SinoMed, and Vip Journal Integration Platform databases were searched from their inception dates to October 2021. Two reviewers independently selected controlled studies evaluating the neurobiological roles of metformin in rats following SCI, extracted data, and assessed the quality of methodology and evidence. Pairwise meta-analyses, subgroup analyses and network analysis were performed to assess the roles of metformin in neurological function and tissue damage in SCI rats. Twelve articles were included in this systematic review. Most of them were of moderate-to-high methodological quality, while the quality of evidence from those studies was not high. Generally, Basso, Beattie, and Bresnahan scores were increased in rats treated with metformin compared with controls, and the weighted mean differences (WMDs) between metformin and control groups exhibited a gradual upward trend from the 3rd (nine studies, n = 164, WMD = 0.42, 95% CI = −0.01 to 0.85, P = 0.06) to the 28th day after treatment (nine studies, n = 136, WMD = 3.48, 95% CI = 2.04 to 4.92, P < 0.00001). Metformin intervention was associated with improved inclined plane scores, tissue preservation ratio and number of anterior horn motor neurons. Subgroup analyses indicated an association between neuroprotection and metformin dose. Network meta-analysis showed that 50 mg/kg metformin exhibited greater protection than 10 and 100 mg/kg metformin. The action mechanisms behind metformin were associated with activating adenosine monophosphate-activated protein kinase signaling, regulating mitochondrial function and relieving endoplasmic reticulum stress. Collectively, this review indicates that metformin has a protective effect on SCI with satisfactory safety and we demonstrate a rational mechanism of action; therefore, metformin is a promising candidate for future clinical trials. However, given the limitations of animal experimental methodological and evidence quality, the findings of this pre-clinical review should be interpreted with caution.

CG7630 is the Drosophila melanogaster homolog of the cytochrome c oxidase subunit COX7B

The mitochondrial respiratory chain (MRC) is composed of four multiheteromeric enzyme complexes. According to the endosymbiotic origin of mitochondria, eukaryotic MRC derives from ancestral proteobacterial respiratory structures consisting of a minimal set of complexes formed by a few subunits associated with redox prosthetic groups. These enzymes, which are the “core” redox centers of respiration, acquired additional subunits, and increased their complexity throughout evolution. Cytochrome c oxidase (COX), the terminal component of MRC, has a highly interspecific heterogeneous composition. Mammalian COX consists of 14 different polypeptides, of which COX7B is considered the evolutionarily youngest subunit. We applied proteomic, biochemical, and genetic approaches to investigate the COX composition in the invertebrate model Drosophila melanogaster. We identified and characterized a novel subunit which is widely different in amino acid sequence, but similar in secondary and tertiary structures to COX7B, and provided evidence that this object is in fact replacing the latter subunit in virtually all protostome invertebrates. These results demonstrate that although individual structures may differ the composition of COX is functionally conserved between vertebrate and invertebrate species.

Mitochondrial ROS signalling requires uninterrupted electron flow and is lost during ageing in flies

Mitochondrial reactive oxygen species (mtROS) are cellular messengers essential for cellular homeostasis. In response to stress, reverse electron transport (RET) through respiratory complex I generates high levels of mtROS. Suppression of ROS production via RET (ROS-RET) reduces survival under stress, while activation of ROS-RET extends lifespan in basal conditions. Here, we demonstrate that ROS-RET signalling requires increased electron entry and uninterrupted electron flow through the electron transport chain (ETC). We find that in old fruit flies, ROS-RET is abolished when electron flux is decreased and that their mitochondria produce consistently high levels of mtROS. Finally, we demonstrate that in young flies, limiting electron exit, but not entry, from the ETC phenocopies mtROS generation observed in old individuals. Our results elucidate the mechanism by which ROS signalling is lost during ageing.

Hemocyte Clusters Defined by scRNA-Seq in Bombyx mori: In Silico Analysis of Predicted Marker Genes and Implications for Potential Functional Roles

Within the hemolymph, insect hemocytes constitute a heterogeneous population of macrophage-like cells that play important roles in innate immunity, homeostasis and development. Classification of hemocytes in different subtypes by size, morphology and biochemical or immunological markers has been difficult and only in Drosophila extensive genetic analysis allowed the construction of a coherent picture of hemocyte differentiation from pro-hemocytes to granulocytes, crystal cells and plasmatocytes. However, the advent of high-throughput single cell technologies, such as single cell RNA sequencing (scRNA-seq), is bound to have a high impact on the study of hemocytes subtypes and their phenotypes in other insects for which a sophisticated genetic toolbox is not available. Instead of averaging gene expression across all cells as occurs in bulk-RNA-seq, scRNA-seq allows high-throughput and specific visualization of the differentiation status of individual cells. With scRNA-seq, interesting cell types can be identified in heterogeneous populations and direct analysis of rare cell types is possible. Next to its ability to profile the transcriptomes of individual cells in tissue samples, scRNA-seq can be used to propose marker genes that are characteristic of different hemocyte subtypes and predict their functions. In this perspective, the identities of the different marker genes that were identified by scRNA-seq analysis to define 13 distinct cell clusters of hemocytes in larvae of the silkworm, Bombyx mori, are discussed in detail. The analysis confirms the broad division of hemocytes in granulocytes, plasmatocytes, oenocytoids and perhaps spherulocytes but also reveals considerable complexity at the molecular level and highly specialized functions. In addition, predicted hemocyte marker genes in Bombyx generally show only limited convergence with the genes that are considered characteristic for hemocyte subtypes in Drosophila.

Anoxia-reoxygenation modulates cadmium-induced liver mitochondrial reactive oxygen species emission during oxidation of glycerol 3-phosphate

Aquatic organisms are frequently exposed to multiple stressors including low dissolved oxygen (O₂) and metals such as cadmium (Cd). Reduced O₂ concentration and Cd exposure alter cellular function in part by impairing energy metabolism and dysregulating reactive oxygen species (ROS) homeostasis. However, little is known about the role of mitochondrial glycerol 3-phosphate dehydrogenase (mGPDH) in ROS homeostasis in fish and its response to environmental stress. In this study, mGPDH activity and the effects of anoxia-reoxygenation (A-RO) and Cd on ROS (as hydrogen peroxide, H₂O₂) emission in rainbow trout liver mitochondria during oxidation of glycerol 3-phosphate (G3P) were probed. Trout liver mitochondria exhibited low mGPDH activity that supported a low respiratory rate but substantial H₂O₂ emission rate. Cd evoked a low concentration stimulatory-high concentration inhibitory H₂O₂ emission pattern that was blunted by A-RO. At specific redox centers, Cd suppressed H₂O₂ emission from site I_Q, but stimulated emission from sites III_Qo and G_Q. In contrast, A-RO stimulated H₂O₂ emission from site I_Q following 15 min exposure and augmented Cd-stimulated emission from site II_F after 30 min exposure but did not alter the rate of H₂O₂ emission from sites III_Qo and G_Q. Additionally, Cd neither altered the activities of catalase, glutathione peroxidase, or thioredoxin reductase nor the concentrations of total glutathione, reduced glutathione, or oxidized glutathione. Overall, this study indicates that oxidation of G3P drives ROS production from mGPDH and complexes I, II and III, whereas Cd directly modulates redox sites but not antioxidant defense systems to alter mitochondrial H₂O₂ emission.

The glutathionylation agent disulfiram augments superoxide/hydrogen peroxide production when liver mitochondria are oxidizing ubiquinone pool-linked and branched chain amino acid substrates

Our group has previously observed that protein S-glutathionylation serves as an integral feedback inhibitor for the production of superoxide (O₂^●-)/hydrogen peroxide (H₂O₂) by α-ketoglutarate dehydrogenase (KGDH), pyruvate dehydrogenase (PDH), and complex I in muscle and liver mitochondria, respectively. In the present study, we hypothesized that glutathionylation would fulfill a similar role for the O₂^●-/H₂O₂ sources sn-glycerol-3-phosphate dehydrogenase (G3PDH), proline dehydrogenase (PRODH), and branched chain keto acid dehydrogenase (BCKDH). Surprisingly, we found that inducing glutathionylation with disulfiram increased the production of O₂^●-/H₂O₂ by mitochondria oxidizing glycerol-3-phosphate (G3P), proline (Pro), or α-keto-β-methylvaleric acid (KMV). Treatment of mitochondria oxidizing G3P or Pro with rotenone or myxothiazol increased the rate of ROS production after incubating in 1000 nM disulfiram. Incubating mitochondria treated with disulfiram in both rotenone and myxothiazol prevented this increase in O₂^●-/H₂O₂ production. In addition, when adminstered together, ROS production decreased below control levels. Disulfiram-treated mitochondria displayed higher rates of ROS production when oxidizing succinate, which was inhibited by rotenone, myxothiazol, and malonate, respectively. Disulfiram also increased ROS production by mitocondria oxidizing KMV. Treatment of mitochondria oxidizing KMV with disulfiram and rotenone or myxothiazol did not alter the rate O₂^●-/H₂O₂ production further when compared to mitochondria treated with disulfiram only. Analysis of BCKDH activity following disulfiram treatment revealed that glutathionylation does not inhibit the enzyme complex, indicating this α-keto acid dehydrogenase is not a target for glutathione modification. However, treatment of mitochondria with rotenone and myxothiazol without disulfiram also augmented ROS production. Overall, we were able to demonstrate for the first time that glutathionylation augments ROS production by the respiratory chain during forward electron transfer (FET) and reverse electron transfer (RET) from the UQ pool. Additionally, we were able to show that BCKDH is not a target for glutathione modification and that glutathionylation can also increase ROS production in mitochondria oxidizing branched chain amino acids following the modification of enzymes upstream of BCKDH.

Mitofusin-2 boosts innate immunity through the maintenance of aerobic glycolysis and activation of xenophagy in mice

Mitochondrial function and innate immunity are intimately linked; however, the mechanisms how mitochondrion-shaping proteins regulate innate host defense remains largely unknown. Herein we show that mitofusin-2 (MFN2), a mitochondrial fusion protein, promotes innate host defense through the maintenance of aerobic glycolysis and xenophagy via hypoxia-inducible factor (HIF)-1α during intracellular bacterial infection. Myeloid-specific MFN2 deficiency in mice impaired the antimicrobial and inflammatory responses against mycobacterial and listerial infection. Mechanistically, MFN2 was required for the enhancement of inflammatory signaling through optimal induction of aerobic glycolysis via HIF-1α, which is activated by mitochondrial respiratory chain complex I and reactive oxygen species, in macrophages. MFN2 did not impact mitophagy during infection; however, it promoted xenophagy activation through HIF-1α. In addition, MFN2 interacted with the late endosomal protein Rab7, to facilitate xenophagy during mycobacterial infection. Our findings reveal the mechanistic regulations by which MFN2 tailors the innate host defense through coordinated control of immunometabolism and xenophagy via HIF-1α during bacterial infection.

Mitochondrial Reactive Oxygen Species Regulate Immune Responses of Macrophages to Aspergillus fumigatus

Reactive Oxygen Species (ROS) are highly reactive molecules that can induce oxidative stress. For instance, the oxidative burst of immune cells is well known for its ability to inhibit the growth of invading pathogens. However, ROS also mediate redox signalling, which is important for the regulation of antimicrobial immunity. Here, we report a crucial role of mitochondrial ROS (mitoROS) in antifungal responses of macrophages. We show that mitoROS production rises in murine macrophages exposed to swollen conidia of the fungal pathogen Aspergillus fumigatus compared to untreated macrophages, or those treated with resting conidia. Furthermore, the exposure of macrophages to swollen conidia increases the activity of complex II of the respiratory chain and raises mitochondrial membrane potential. These alterations in mitochondria of infected macrophages suggest that mitoROS are produced via reverse electron transport (RET). Significantly, preventing mitoROS generation via RET by treatment with rotenone, or a suppressor of site IQ electron leak, S1QEL1.1, lowers the production of pro-inflammatory cytokines TNF-α and IL-1β in macrophages exposed to swollen conidia of A. fumigatus. Rotenone and S1QEL1.1 also reduces the fungicidal activity of macrophages against swollen conidia. Moreover, we have established that elevated recruitment of NADPH oxidase 2 (NOX2, also called gp91phox) to the phagosomal membrane occurs prior to the increase in mitoROS generation. Using macrophages from gp91phox-/- mice, we have further demonstrated that NOX2 is required to regulate cytokine secretion by RET-associated mitoROS in response to infection with swollen conidia. Taken together, these observations demonstrate the importance of RET-mediated mitoROS production in macrophages infected with A. fumigatus.

Dramatic changes in mitochondrial substrate use at critically high temperatures: a comparative study using Drosophila

Ectotherm thermal tolerance is critical to species distribution, but at present the physiological underpinnings of heat tolerance remain poorly understood. Mitochondrial function is perturbed at critically high temperatures in some ectotherms, including insects, suggesting that heat tolerance of these animals is linked to failure of oxidative phosphorylation (OXPHOS) and/or ATP production. To test this hypothesis, we measured mitochondrial oxygen consumption rate in six Drosophila species with different heat tolerance using high-resolution respirometry. Using a substrate-uncoupler-inhibitor titration protocol, we examined specific steps of the electron transport system to study how temperatures below, bracketing and above organismal heat limits affect mitochondrial function and substrate oxidation. At benign temperatures (19 and 30°C), complex I-supported respiration (CI-OXPHOS) was the most significant contributor to maximal OXPHOS. At higher temperatures (34, 38, 42 and 46°C), CI-OXPHOS decreased considerably, ultimately to very low levels at 42 and 46°C. The enzymatic catalytic capacity of complex I was intact across all temperatures and accordingly the decreased CI-OXPHOS is unlikely to be caused directly by hyperthermic denaturation/inactivation of complex I. Despite the reduction in CI-OXPHOS, maximal OXPHOS capacity was maintained in all species, through oxidation of alternative substrates - proline, succinate and, particularly, glycerol-3-phosphate - suggesting important mitochondrial flexibility at temperatures exceeding the organismal heat limit. Interestingly, this failure of CI-OXPHOS and compensatory oxidation of alternative substrates occurred at temperatures that correlated with species heat tolerance, such that heat-tolerant species could defend 'normal' mitochondrial function at higher temperatures than sensitive species. Future studies should investigate why CI-OXPHOS is perturbed and how this potentially affects ATP production rates.

Coenzyme Q redox signalling and longevity

Mitochondria are the powerhouses of the cell. They produce a significant amount of the energy we need to grow, survive and reproduce. The same system that generates energy in the form of ATP also produces Reactive Oxygen Species (ROS). Mitochondrial Reactive Oxygen Species (mtROS) were considered for many years toxic by-products of metabolism, responsible for ageing and many degenerative diseases. Today, we know that mtROS are essential redox messengers required to determine cell fate and maintain cellular homeostasis. Most mtROS are produced by respiratory complex I (CI) and complex III (CIII). How and when CI and CIII produce ROS is determined by the redox state of the Coenzyme Q (CoQ) pool and the proton motive force (pmf) generated during respiration. During ageing, there is an accumulation of defective mitochondria that generate high levels of mtROS. This causes oxidative stress and disrupts redox signalling. Here, we review how mtROS are generated in young and old mitochondria and how CI and CIII derived ROS control physiological and pathological processes. Finally, we discuss why damaged mitochondria amass during ageing as well as methods to preserve mitochondrial redox signalling with age.

Structural basis for a complex I mutation that blocks pathological ROS production

Mitochondrial complex I is central to the pathological reactive oxygen species (ROS) production that underlies cardiac ischemia-reperfusion (IR) injury. ND6-P25L mice are homoplasmic for a disease-causing mtDNA point mutation encoding the P25L substitution in the ND6 subunit of complex I. The cryo-EM structure of ND6-P25L complex I revealed subtle structural changes that facilitate rapid conversion to the "deactive" state, usually formed only after prolonged inactivity. Despite its tendency to adopt the "deactive" state, the mutant complex is fully active for NADH oxidation, but cannot generate ROS by reverse electron transfer (RET). ND6-P25L mitochondria function normally, except for their lack of RET ROS production, and ND6-P25L mice are protected against cardiac IR injury in vivo. Thus, this single point mutation in complex I, which does not affect oxidative phosphorylation but renders the complex unable to catalyse RET, demonstrates the pathological role of ROS production by RET during IR injury.

Novel Insights Into Molecular Mechanism of Mitochondria in Diabetic Cardiomyopathy

Cardiovascular complication is one of the significant causes of death in diabetic mellitus (DM) in which diabetic cardiomyopathy, independent of hypertension, cardiac valvular disease, and coronary atherosclerosis, occupies an important position. Although the detailed pathogenesis of diabetic cardiomyopathy remains unclear currently, mitochondrial morphological abnormality and dysfunction were observed in diabetic cardiomyopathy animal models according to much research, suggesting that mitochondrial structural and functional impairment played an integral role in the formation of diabetic cardiomyopathy. Thus, we have summarized the effect of mitochondria on the process of diabetic cardiomyopathy, including abnormal mitochondrial morphology, mitochondrial energy metabolism disorder, enhanced mitochondrial oxidative stress, mitochondrial unbalanced calcium homeostasis, and mitochondrial autophagy. Based on the above mechanisms and the related evidence, more therapeutic strategies targeting mitochondria in diabetic cardiomyopathy have been and will be proposed to delay the progression of the disease.

Is the NDUFV2 subunit of the hydrophilic complex I domain a key determinant of animal longevity?

Complex I, a component of the electron transport chain, plays a central functional role in cell bioenergetics and the biology of free radicals. The structural and functional N module of complex I is one of the main sites of the generation of free radicals. The NDUFV2 subunit/N1a cluster is a component of this module. Furthermore, the rate of free radical production is linked to animal longevity. In this review, we explore the hypothesis that NDUFV2 is the only conserved core subunit designed with a regulatory function to ensure correct electron transfer and free radical production, that low gene expression and protein abundance of the NDUFV2 subunit is an evolutionary adaptation needed to achieve a longevity phenotype, and that these features are determinants of the lower free radical generation at the mitochondrial level and a slower rate of aging of long-lived animals.

Context-dependent responses of Drosophila intestinal stem cells to intracellular reactive oxygen species

Reactive oxygen species (ROS) contribute to cellular redox environment and serve as signaling molecules. Excessive ROS can lead to oxidative stress that are involved in a broad spectrum of physiological and pathological conditions. Stem cells have unique ROS regulation while cancer cells frequently show a constitutive oxidative stress that is associated with the invasive phenotype. Antioxidants have been proposed to forestall tumor progression while targeted oxidants have been used to destroy tumor cells. However, the delicate beneficial range of ROS levels for stem cells and tumor cells under distinct contexts remains elusive. Here, we used Drosophila midgut intestinal stem cell (ISCs) as an in vivo model system to tackle this question. The ROS levels of ISCs remained low in comparison to that of differentiated cells and increased with ageing, which was accompanied by elevated proliferation of ISCs in aged Drosophila. Neither upregulation nor downregulation of ROS levels significantly affected ISCs, implicating an intrinsic homeostatic range of ROS in ISCs. Interestingly, we observed similar moderately elevated ROS levels in both tumor-like ISCs induced by Notch (N) depletion and extracellular matrix (ECM)-deprived ISCs induced by β-integrin (mys) depletion. Elevated ROS levels further promoted the proliferation of tumor-like ISCs while reduced ROS levels suppressed the hyperproliferation phenotype; on the other hand, further increased ROS facilitated the survival of ECM-deprived ISCs while reduced ROS exacerbated the loss of ECM-deprived ISCs. However, N- and mys-depleted ISCs, which resembled metastatic tumor cells, harbored even higher ROS levels and were subjected to more severe cell loss, which could be partially prevented by ectopic supply of antioxidant enzymes, implicating a delicate pro-surviving and proliferating range of ROS levels for ISCs. Taken together, our results revealed stem cells can differentially respond to distinct ROS levels under various conditions and suggested that the antioxidant-based intervention of stem cells and tumors should be formulated with caution according to the specific situations.

An Update on Mitochondrial Reactive Oxygen Species Production

Mitochondria are quantifiably the most important sources of superoxide (O₂^●-) and hydrogen peroxide (H₂O₂) in mammalian cells. The overproduction of these molecules has been studied mostly in the contexts of the pathogenesis of human diseases and aging. However, controlled bursts in mitochondrial ROS production, most notably H₂O₂, also plays a vital role in the transmission of cellular information. Striking a balance between utilizing H₂O₂ in second messaging whilst avoiding its deleterious effects requires the use of sophisticated feedback control and H₂O₂ degrading mechanisms. Mitochondria are enriched with H₂O₂ degrading enzymes to desensitize redox signals. These organelles also use a series of negative feedback loops, such as proton leaks or protein S-glutathionylation, to inhibit H₂O₂ production. Understanding how mitochondria produce ROS is also important for comprehending how these organelles use H₂O₂ in eustress signaling. Indeed, twelve different enzymes associated with nutrient metabolism and oxidative phosphorylation (OXPHOS) can serve as important ROS sources. This includes several flavoproteins and respiratory complexes I-III. Progress in understanding how mitochondria generate H₂O₂ for signaling must also account for critical physiological factors that strongly influence ROS production, such as sex differences and genetic variances in genes encoding antioxidants and proteins involved in mitochondrial bioenergetics. In the present review, I provide an updated view on how mitochondria budget cellular H₂O₂ production. These discussions will focus on the potential addition of two acyl-CoA dehydrogenases to the list of ROS generators and the impact of important phenotypic and physiological factors such as tissue type, mouse strain, and sex on production by these individual sites.